Combination Treatment to Improve Mucociliary Transport of Pseudomonas aeruginosa Biofilms

People with muco-obstructive pulmonary diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) often have acute or chronic respiratory infections that are difficult to treat due in part to the accumulation of hyperconcentrated mucus within the airway. Mucus accumulation and obstruction promote chronic inflammation and infection and reduce therapeutic efficacy. Bacterial aggregates in the form of biofilms exhibit increased resistance to mechanical stressors from the immune response (e.g., phagocytosis) and chemical treatments including antibiotics. Herein, combination treatments designed to disrupt the mechanical properties of biofilms and potentiate antibiotic efficacy are investigated against mucus-grown Pseudomonas aeruginosa biofilms and optimized to 1) alter biofilm viscoelastic properties, 2) increase mucociliary transport rates, and 3) reduce bacterial viability. A disulfide bond reducing agent (tris(2-carboxyethyl)phosphine, TCEP), a surfactant (NP40), a biopolymer (hyaluronic acid, HA), a DNA degradation enzyme (DNase), and an antibiotic (tobramycin) are tested in various combinations to maximize biofilm disruption. The viscoelastic properties of biofilms are quantified with particle tracking microrheology and transport rates are quantified in a mucociliary transport device comprised of fully differentiated primary human bronchial epithelial cells. The combination of the NP40 with hyaluronic acid and tobramycin was the most effective at increasing mucociliary transport rates, decreasing the viscoelastic properties of mucus, and reducing bacterial viability. Multimechanistic targeting of biofilm infections may ultimately result in improved clinical outcomes, and the results of this study may be translated into future in vivo infection models. Author SummaryOne of the major challenges associated with chronic respiratory infections in cystic fibrosis and chronic obstructive pulmonary disease is difficult to treat biofilms that form in hyperconcentrated mucus. Biofilms are mechanically robust due to an exterior polymeric matrix that protects from the immune response and antibiotics. Antibiotics like tobramycin alone have little impact on the biofilm matrix, but disruption of viscous mucus and the biofilm architecture has previously been shown to improve antibiotic efficacy. Combination treatments must be used to break up mucus and biofilms and simultaneously kill bacteria. The most promising combination in this study includes the surfactant NP40, the biopolymer hyaluronic acid, and the antibiotic tobramycin which together decreased biofilm viscosity, reduced bacterial load, and increased mucociliary transport rates. The results from this study may be translated to an infected animal study for eventual clinical trials.